Electromagnetic flow meter

ABSTRACT

An electromagnetic flow meter utilizing Faraday&#39;&#39;s law is disclosed. The flow meter transmitter has a magnetic field forming means including a core, which is a cast core made of a ferromagnetic material containing silicon.

Unite States atent n91 Kawamata et an.

[11] 3,827,298 [451 Aug. 6, 1974 ELECTROMAGNETIC FLOW METER Inventors:lsamu Kawamata; Mitsuo Ai, both of Katsuta; Ichiya Satoh, Hitachi, all

of Japan Assignee: Hitachi Ltd., Tokyo, Japan Filed: Oct. 26, 1972 Appl.No.: 300,890

Foreign Application PriorityvData Oct. 29, 1971 Japan 46-85505 US. Cl.,73/194 EM, 335/297 Int. Cl. GOlf 1/00 Field of Search 73/194 EM;336/233, DIG. 3; 335/297; 29/607 [56] References Cited UNITED STATESPATENTS I 3,255,512 6/1966 Lochner et a1. 336/233 X 3,446,071 5/1969Kolin et al. 73/194 EM 3,527,095 9/1970 Wada 73/194 EM 3,608,375 9/1971Cushing 73/194 EM 3,610,040 10/1971 Wada 73/194 EM PrimaryExaminer-Charles A. Ruehl Attorney, Agent, or Firm-Craig & Antonelli [57] ABSTRACT An electromagnetic flow meter utilizing Faradays law isdisclosed. The flow meter transmitter has a magnetic field forming meansincluding a core, which is a cast core made of a ferromagnetic materialcontaining silicon.

9 Claims, 8 Drawing Figures PAIENTEDMJB m 3.827. 298

SHEEI 1 BF 4 F l G lb PRIOR ART l" f7 FlG.|c E 'HHI'HMHW E PR'OR ARTIll.

PATENIED 51974 3,827. 298

' sum 3 or 4 ELECTROMAGNETIC rrow METER This invention relates to fieldforming means for electromagnetic flow maters utilizing Faradays law.

The core in the field forming means used in electromagnetic flow metershas heretofore been formed by laminating E-shaped silicon steel platesproduced by die stamping. Therefore, the material utilization factor hasbeen low and uneconomical.

Besides, with the laminated core it is very difficult to obtain uniformfields due to structural methods, and this leads to the generation of anoise voltage after assemblage of the field forming means.

An object of the invention is to provide an electromagnetic flow meter,which can overcome the aforementioned drawbacks inherent in theprior-art electromagnetic flow meter using a laminated core, and withwhich it is possible to ensure effective and economical materialutilization, constant loss, readily set up uniform magnetic fields andfreedom from generation of noise voltage after assemblage, particularlyafter disassemblage and reassemblage.

The invention is based on the recognition that the flux density of themagnetic field used in electromagnetic flow meters is usually low, andits feature resides in a cast core, which is either a cast iron castcore or a pure iron cast core or is made by bending at least one rolledpure iron plate or by grinding a pure iron rod or a pure iron pipe orfrom a ferromagnetic material containing silicon in addition to suchelements as nickel and chromium.

In the drawing;

FIGS. la, lb and show a flow meter;

FIGS. 2a and 2b illustrate principles underlying the generation of noisevoltages 90 out of phase with the signal voltage;

FIG. 3 shows an embodiment of the invention; and

FIGS. 4a and 4b show flux distributions obtained with theelectromagnetic flow meter of FIG. 3.

FIG. 1a is a front view of a prior-art electromagnetic flow meter, FIG.lb is a fragmentary side view of the same flow meter, and FIG. 1c is anenlarged view of a part indicated at a in FIG. 1b. Referring to theseFigures, numeral l designates a non-magnetic pipe through whichconductive fluid flows. Numeral 2 designates alining provided on theinner surface of the pipe 1, numeral 3 a pair of electrodes, numeral 4leads leading from these electrodes, numeral 5 an exciting coil, numeral6 a core, numeral 7 fixing metals, and numeral 8 bolts.

In the exciting portion, usually an E-type core is used as shown in FIG.la. Since this type of core is formed by die stamping, its materialutilization factor is low, which is uneconomical.

Also, since the core 6 consists of a lamination of thin silicon steelplates fastened by means of bolts 8, the apparent effective core spacefactor and hence the loss in the individual silicon steel plates varieswith the extent of fastening of the nuts on the bolts and fluctuationsof the thickness of the insulating film applied on each silicon steelplate. Further, the edge of the magnetic path after assemblage is likelyto have an irregular form as shown in FIG. 1c. From the above grounds,with the prior-art magnetic circuit using silicon steel plates it isextremely difficult to obtain a uniform magnetic field, and theseindividual problems would lead to the generprior-art electromagnetication of noise voltage after assemblage as will be describedhereinafter.

FIG. 2a shows the principles of generation of noise voltage out of phasewith the signal voltage. As is seen, the leads 4 from the electrodes Edform one turn through the fluid, so that noise voltage is given rise toas magnetic flux links with them. Particularly, this noise generation iscaused where the angle 0 between the pipe axis X, and core axis Yrepresenting the field direction is not a right angle. In the Figures,the same reference numerals as in FIG. 1 designate like parts. Numeral 9designates a transmitter.

FIG. 2b shows an equivalent circuit for the system of FIG. 2a. In theFigure, reference character R designates exciting coil resistance,character R, loss resistance, character L exciting coil inductance,character (I) magnetic flux, character P pipe, and character e, signalvoltage.

In another aspect, with the laminated core it is difficult to obtaininterchangeability between generator and transmitter due to theaforementioned fluctuations and irregularities.

As has been shown, while the prior-art laminated core has an inherentmerit in that loss is small, it has a demerit in that it is difficult toobtain a uniform field due to structural methods.

The cast core, on the other hand, is mechanically very strong and easilyprocessible, but it has a problem in that ef due to iron loss tends tobe large. This means that the cast core would be preferred if thisproblem could be solved. The output of an electromagnetic flow metertransmitter is usually given as the ratio between flow signal voltageand exciting current, and the value ef when the source frequency ischanged from f to f; is given, with reference to FIG. 2b, from anequation To reduce ef in equation (1) the loss resistance R, may beincreased, and to this end the iron loss should be reduced. Among theiron losses (hysteresis loss, eddy current loss), it is eddy currentloss that constitutes a problem. The eddy current loss W is given aswhere f is frequency, t is core thickness, p is resistivity of the core,Bm is flux density and K is a proportionality constant.

It will be seen from equation (2) that to make W small it is necessaryto select the core material such that t is small and p is large, sinceBm depends upon the aperture of the electromagnetic flow meter. In thecase of electromagnetic flow meters, the flux density is low, so thatwith a flow meter aperture of, for instance, 25 mm the core thicknessmay be made as small as about 5 mm, and the resistivity p of the coremay be increased by the incorporation of nickel, chromium and siliconand spheroidizing of carbon, whereby reduction of the eddy current lossW may be achieved. The following table lists characteristic values of anexample with a flow meter aperture of 25 mm.

TABLE Inductance L,,: 248 mH Loss resistance R, 512 ohms Iron loss R18.5 W

sf effect: 1 0.19 percent (for a change of: 2 Hz) In this example, if iswithin i 0.2 percent for a change of It 2H2, and it will lead to nopractical problems.

With a structure integrally having core and coil to be describedhereinafter, it is possible to provide an electromagnetic flow meterwhere the value of ef due to assemblage and disassemblage is with i 0.3percent.

In practice, if is no problem if it is within 1*: 0.5 percent for achange of i 2 B2. A preferred composition of the field forming portionto obtain the above characteristic values will be 96.1 percent iron, 3.5percent silicon, 4.0 percent spheroidized carbon, 0.9 percent manganese, and slight quantities of nickel and chromium. The incorporationof nickel and chromium gives good effect upon the improvement of thecharacteristics.

An embodiment of the invention will now be described with reference toFIG. 3. FIG. 3 shows the construction. The same reference numerals asthose in FIG. 1 designate like parts.

As is, shown, according to the invention the portions of the core wherethe magnetic fluxes emerge therefrom or return thereto is constructedsuch that the magnetic reluctance is distributed symmetrically withrespect to line a-a' in FIG. 3, with pole faces 9,9 opposing andextending parallel to each other for impressing the magnetic field inthe vertical direction of the pipe are machine finished to eliminatesurface irregularities, and is formed such as to minimize the magneticpath length I.

Also, according to the invention the exciting coil 5 is held integralwith the core or outer core 6, which, unlike the prior-artelectromagnetic flow meters, is made of cast iron cast core or pure ironcast core or is made by bending at least one rolled pure iron plate orby grinding a pure iron rod or a pure iron pipe or from a ferromagneticmaterial containing silicon in addition to such elements as nickel andchromium. The relative positions of the coil 5 and core 6 are fixed byfixing metals 7.

In this embodiment, the core consists of two parts, namely upper andlower halves, extending along the pole faces forming the field. Thisconstruction is advantageous in that the lower core half with theassociated coil can be removed in the integral state, with the upperhalf provided with signal take-out leads held fixed, by

merely loosening nuts on bolts 8, and at the time of reassemblage thecharacteristics before the disassemblage can be readily reproduced.Another advantage is that by virture of the integral arrangement of thecore and exciting coil, the field will not be prone to irregularities orvariations.

It is to be emphasized that according to the invention it is essentiallypossible to reproduce various electric characteristics because of thecapability of machining the core.

Also, according to the invention a uniform field may be readily obtainedwith extremely small field fluctuations.

invention along three perpendicular axes X-X 7 Y--Y' and Z-Zintersecting at the origin 0 as shown in FIG. 4b. In the case of the25-min electromagentic flow meter, it is practically sufficient if thefield is uniform over a region as indicated at A.

Further, since the core according to the invention is a single cast coreor may be made of cast steel or pure iron, the material control touniformalize the loss can be readily done.

The illustrated configuration of the core is not given in a limitativesense, but it is possible to have a ring-like cast core form. Also, theopposing pole faces need not be parallel to each other.

Further, the core construction consisting of upper and lower core halves6 and 6 shown in FIG. 3 is by no means limitative, but any othersuitable core construction consisting of at least two parts may beemployed provided that the disassemblage and reassemblage are possible.

Furthermore, the construction of FIG. 3 even permits the use of usualsilicon steel plates. For example, two

or three steel plates thicker than 0.35 to 0.5 mm and thinner than 5 to6 mm may be used in the stacked form. Still further, the core dimensionin the direction of the pipe, that is, core width w, need not beconstant. In other words, the core may consist of a plurality ofsections with a width of w, w/2, w/3, etc. At any rate, it is possibleto readily form a uniform field with a simple construction compared tothe prior-art laminated core.

Further, the invention may as well be applied where field intensities ashigh as 1,000 to 2,000 gauss are dealt with and to large apertureelectromagnetic flow meters, for instance with an aperture of 1,000 mm.Furthermore, the elements that are to be incorporated to increase theresistivity of the cast core are not limited to nickel, chromium andsilicon alone, but any other suitable element may be incorporated.Moreover, through the incorporation of spheriodized carbon intothe castcore it is possible to obtain electromagnetic flow meters with a castcore having improved wear resistance, heat resistance and mechanicalstrength as well as increased resistivity.

As has been described in the foregoing, according to the invention theintended results may be fully achieved not with a laminated core butwith a cast core or the like.

What is claimed is:

1. An electromagnetic flow meter comprising a pipe through which a fluidis adapted to flow, magnetic means for applying magnetic fluxes to thefluid in a direction substantially perpendicular to the direction offlow of the fluid through said pipe and a pair of electrodeselectrically connected to the fluid for detecting an electrical signalrelating to the flow rate of the fluid through said pipe, said magneticmeans including a magnetic core and an exciting coil integrally mountedin said magnetic core, said magnetic core being a cast core of aferromagnetic material containing silicon.

2. The electromagnetic flow meter according to claim 1, wherein saidferromagnetic material further contains at least one of manganese andchromium.

3. The electromagnetic flow meter according to claim 1, wherein saidferromagnetic material further contains spheriodized carbon.

4. The electromagnetic flow meter according to claim '1, wherein saidmagnetic core is formed to surround said pipe substantiallysymmetrically with respect to the center of said pipe.

5. The electromagnetic flow meter according to claim 4, wherein saidcore has a pair of pole faces for applying the magnetic fluxes, saidpole faces extending parallel to each other.

6. The electromagnetic flow meter according to claim 1, wherein saidmagnetic core comprises two portions which are mounted thereinintegrally with respective portions of said coil and are detachablyconnected to each other together with the associated portion of saidexciting coil.

7. The electromagnetic flow meter according to ll'Oll.

1. An electromagnetic flow meter comprising a pipe through which a fluidis adapted to flow, magnetic means for applying magnetic fluxes to thefluid in a direction substantially perpendicular to the direction offlow of the fluid through said pipe and a pair of electrodeselectrically connected to the fluid for detecting an electrical signalrelating to the flow rate of the fluid through said pipe, said magneticmeans including a magnetic core and an exciting coil integrally mountedin said magnetic core, said magnetic core being a cast core of aferromagnetic material containing silicon.
 2. The electromagnetic flowmeter according to claim 1, wherein said ferromagnetic material furthercontains at least one of manganese and chromium.
 3. The electromagneticflow meter according to claim 1, wherein said ferromagnetic materialfurther contains spheriodized carbon.
 4. The electromagnetic flow meteraccording to claim 1, wherein said magnetic core is formed to surroundsaid pipe substantially symmetrically with respect to the center of saidpipe.
 5. The electromagnetic flow meter according to claim 4, whereinsaid core has a pair of pole faces for applying the magnetic fluxes,said pole faces extending parallel to each other.
 6. The electromagneticflow meter according to claim 1, wherein said magnetic core comprisestwo portions which are mounted therein integrally with respectiveportions of said coil and are detachably connected to each othertogether with the associated portion of said exciting coil.
 7. Theelectromagnetic flow meter according to claim 1, wherein said magneticcore comprises two portions each having a pole face, said two portionsbeing detachably connected to each other along a sectional planeextending in the direction parallel to the surface of said pole face. 8.The electromagnetic flow meter according to claim 7, further comprisingmetal plate members extending outwardly beyond each pole face forpositioning and securing said exciting coil within said magnetic core.9. The electromagnetic flow meter according to claim 1, wherein saidferromagnetic material comprises iron.